Endoscopes are commonly used to view the interior passage of an object. Endoscopes have industrial applications wherein the endoscope is used to view a passage within, for example, a piece of equipment. Endoscopes also have medical applications wherein the endoscope is used to view a passage within the body of a patient.
An endoscope typically includes an endoscope body and optical components carried by the endoscope body to enable viewing of the passage distally of the distal end of the endoscope body. The optical components may include illumination optics for illuminating the field of view, and such illumination optics may comprise optical fibers carried by the endoscope body.
The optical components also include the optics necessary to transmit or relay an image proximally and to provide the image to an eyepiece for direct visualization or to a camera which enables viewing of the scene on a TV monitor. These latter optics may include an elongated fiberoptic image guide, comprising a fiberoptic imaging bundle having a plurality of fibers for transmitting the image proximally, a distal objective lens system located adjacent to the distal end of the fiberoptic image guide, and an ocular lens assembly adjacent the proximal end of the endoscope body.
A characteristic of endoscopes of this type is that the fibers in such devices typically have a relatively high (0.30 to 0.50) numerical aperture in order to capture as much light as possible from the subject. Additionally, the ocular lens assembly typically comprises an eyepiece lens having a high magnification power. The high numerical aperture together with the small diameter of the fibers and the high magnification power of the eyepiece lens tends to result in a very shallow depth of focus at the eyepiece. In other words, very small linear shifts of the proximal end of the image guide with respect to the eyepiece lens can cause the image to quickly become out of focus because of the shallow depth of focus of the eyepiece lens. This is critical when focusing effects are present which tend to cause the distance between the eyepiece lens and the proximal end of the image guide to vary. Such focusing effects may include thermal expansion of the length of the fiber optic bundle or mechanical tolerances on the placement of the ocular lens assembly elements, for example.
Another aspect involves subjecting the endoscope or components thereof to varying temperatures. For example, endoscopes for medical use are typically reusable. Between uses it is desirable to sterilize the endoscope, for example, at elevated temperatures. Since the endoscope is typically constructed from materials having varying coefficients of thermal expansion, prolonged exposure to heat can damage the mechanical as well as the optical integrity of the endoscope. In addition, in other (non-medical) use applications, endoscopes may be subjected to varying temperatures, such as use at quite elevated temperatures followed by storage at room temperature, or use at two or more different temperatures. Because of such temperature differences, mechanical and/or optical damage to the scope can result.
One type of fiberoptic image guide utilizes at least partially non-fused image fibers which, because of its inherent flexibility, can accommodate any longitudinal translation. However, from a cost and manufacturing standpoint, fiberoptic image guides made from at least partially non-fused fibers are not practical. Due to their inherent fragility, the manufacturing costs are high and they are typically characterized by low resolution.
Alternately, scopes which utilize entirely fused fiberoptic image guides may be made from 1,000 to 60,000 individual fibers and are particularly useful in small sizes which cannot be sufficiently managed by classical glass lens technology. These image guides can be incorporated into flexible or rigid endoscope systems. To consistently maintain optical and mechanical integrity, these image guides are typically bonded at both ends, proximal and distal, to the endoscope body or sheath. A distal lens assembly, which is fixed to the endoscope body, is located distally of the image guide. The proximal portion of the fiberoptic image guide is fixed to the endoscope body so that a repeatable connection to a camera coupling or eyepiece can be made. One limitation of this type of endoscope system is that during temperature change the fiberoptic bundle may expand at a different rate relative to the body or sheath to which it is bonded and, in so doing, cause mechanical and/or optical damage to the endoscope.
One method which has been suggested to accommodate the expansion properties of a fused fiberoptic image guide and endoscope body is to build into the design an area for relaxation in the image guide to take place. However, curved portions of an image guide are not always possible or practical. Larger diameter guides are inherently less flexible or readily curvable within the endoscope body or sheath. From a practical standpoint, medical endoscopes are purposely designed to use a minimal amount of space to allow for easier access to smaller areas of the body and smaller insertion modalities. Providing an endoscope design with sufficient area for accommodating a curved image guide would not be space efficient.
Therefore, it would be advantageous to provide an endoscope which can be subjected to prolonged exposure at varying temperatures, for example, during sterilization or use, without damaging the mechanical and/or optical integrity of the endoscope.
It would additionally be advantageous to provide an endoscope which is capable of a much larger tolerance for focusing effects such as thermal expansion of the length of the fiber optic bundle or mechanical tolerances on the placement of the ocular lens elements, without focus adjustment. This would, for example, permit the interchange of fiberoptic bundles on a fixed-focus eyepiece without excessively tight mechanical tolerances.